1. Field of the Invention
The present invention relates to a hybrid vehicle and a method of controlling the hybrid vehicle. More specifically the invention pertains to a hybrid vehicle with an engine that outputs power through combustion of a fuel, a generator that generates electric power with at least part of the power output from the engine, and a motor that outputs power to a drive shaft of the vehicle, as well as a method of controlling such a hybrid vehicle.
2. Description of the Related Art
A diversity of hybrid vehicles have been proposed. The hybrid vehicle has a motor that outputs electric power as a driving force, in addition to an engine that outputs power through combustion of a fuel, such as gasoline. The hybrid vehicle uses the engine as the final energy source and thus requires only the supply of gasoline or another fuel. It is accordingly not required to socially provide new facilities and equipment, for example, power stations for charging batteries.
The hybrid vehicles are mainly classified into series hybrid vehicles and parallel hybrid vehicles. The series hybrid vehicle uses all the power output from the engine to drive a generator, accumulates the electric power generated by the generator in a battery, and obtains the required driving force to be output to the drive shaft from a motor, which is driven with the electric power accumulated in the battery. The parallel hybrid vehicle has a three shaft-type power distributing mechanism or a pair-rotor motor to distribute the power of the engine, for example, a gasoline engine, and causes the power output from the engine to supply part of the driving force to be output to the drive shaft. In the parallel hybrid vehicle, the residual power that is not output to the drive shaft is used for power generation by the generator. The generated electric power is generally accumulated in a battery or a high-capacity capacitor.
The electric power accumulated in the secondary battery or the high-capacity capacitor is used to drive the vehicle while the engine is at a stop. When the engine is driven but the driving force of the engine does not satisfy all the required torque, the motor utilizes the accumulated electric power to supplement the insufficient torque.
In the hybrid vehicle of the above structure, in the case of malfunction of the secondary battery or the high-capacity capacitor that accumulates the electric power therein or in the case of malfunction of a charging circuit for charging the secondary battery or the high-capacity capacitor, operation of the generator is not allowed. This makes a further drive of the vehicle difficult. According to the principles of the hybrid vehicle, the vehicle can be driven by directly connecting the generator with the motor and driving the motor with the generated electric power. The drive mode in this state is called the battery-less drive mode. In the case where the vehicle is actually driven in the direct connection of the generator with the motor, however, expected abrupt variations in loading on the motor during a drive cause a diversity of problems and troubles. There is a possibility that the loading or the required power of the drive shaft during a drive abruptly decreases within a very short time, due to racing of wheels or any braking operation. In such cases, the electric current to be flown into the motor also abruptly decreases within a very short time. The abrupt decrease in required electric current causes a high impedance in the generator that is driven in stationary state by the engine. This abruptly raises the voltage between terminals of the generator and causes an unexpectedly high voltage to be applied to the circuit and exceed the rated power of the circuit.
In the actual state, these problems make the battery-less drive mode substantially unpractical. It is difficult to actualize the limp home capability that enables the vehicle to be anyway driven to a gas station while the battery or its charging circuit malfunctions. Especially in the case of malfunction of a switching element included in an inverter that is connected to the generator to form the charging circuit, even when the engine, the generator, and the motor are all normally operable, the vehicle is driven only with the electric power accumulated in the battery. This undesirably leads to a restricted driving distance or a limited vehicle speed.
The secondary battery used in the hybrid vehicle is a high voltage battery. Positive and negative power lines respectively have contacts to cut off the connection of the power lines with the secondary battery in the inactive state. These contacts are kept open when the vehicle is not used or when some abnormality is detected in the battery. The open position of the contacts prevents the high voltage of the secondary battery from being applied to the power lines when not required. These contacts are used to allow and forbid a large flow of electric current and are thereby often subject to troubles like welding. The prior art arrangement accordingly connects the power line with a standard contact in parallel via a resistor for restricting the electric current and an auxiliary contact. The procedure first closes the auxiliary contact to allow a restricted flow of electric current and then closes the standard contact.
In this prior art arrangement, however, there is still a possibility that the contact welds. In response to detection of a weld of the contact in either one of the positive and negative power lines, the prior art arrangement prohibits the use of the secondary battery. If the continuous use of the secondary battery is allowed in the welding state of one contact, the connection of the secondary battery with the power lines can not be cut off in case of a weld of the other contact.
The object of the present invention is thus to attain a drive of a hybrid vehicle with an engine, a generator, and a motor mounted thereon without using a secondary battery.
At least part of the above and the other related objects is actualized by a first hybrid vehicle with an engine, a generator, and a motor mounted thereon, wherein the engine outputs power through combustion of a fuel, the generator provided with permanent magnets generates electric power with at least part of the power output from the engine, and the motor outputs power to a drive shaft of the hybrid vehicle. The first hybrid vehicle includes: an engine control unit that feedback controls a quantity of the fuel injected to the engine to attain a specified target revolving speed of the engine; a power generation control unit that causes the generator to carry out power generation utilizing a counter electromotive force; a loading detection unit that specifies a loading applied to the hybrid vehicle; a generator rotational speed variation unit that varies a rotational speed of the generator, based on the specified loading; and a motor driving unit that drives the motor with the electric power generated by the generator at the varying rotational speed.
There is also a method of controlling the hybrid vehicle, which corresponds to the arrangement of the first hybrid vehicle. The present invention is accordingly directed to a first method of controlling a hybrid vehicle, wherein an engine outputs power through combustion of a fuel, a generator provided with permanent magnets generate electric power with at least part of the power output from the engine, and a motor is driven with at least part of the electric power generated by the generator, so as to output power to a drive shaft of the vehicle. The first method includes the steps of: feedback controlling a quantity of the fuel injected to the engine to attain a specified target revolving speed of the engine; causing the generator to carry out power generation utilizing a counter electromotive force; specifying a loading applied to the hybrid vehicle; varying a rotational speed of the generator, based on the specified loading; and driving the motor with the electric power generated by the generator at the varying rotational speed.
The first hybrid vehicle of the present invention or the corresponding first method of controlling the hybrid vehicle feedback controls the quantity of the fuel injected to the engine, in order to make the actual revolving speed of the engine coincident with a specified target revolving speed. This arrangement effectively prevents the revolving speed of the engine from varying with a variation in loading of the generator, which generates electric power with at least part of the power output from the engine. While the generator carries out power generation utilizing a counter electromotive force, the motor consumes the electric power generated by the generator and carries out the power operation. The rotational speed of the generator is varied according to the loading applied to the vehicle. This arrangement enables the adequate power corresponding to the loading of the vehicle to be output to the drive shaft of the vehicle. The arrangement of varying the rotational speed of the generator with a variation in loading applied to the vehicle effectively prevents the rotational speed of the generator from being unnecessarily heightened under the condition of low loading.
In accordance with one preferable application of the present invention, the hybrid vehicle further includes: an inverter that switches electric current running through a multiphase coil of the generator; and a secondary battery that is charged with the direct current converted by the switching operation of the inverter. The control procedure causes the power generation control unit, the generator rotational speed variation unit, and the motor driving unit to implement their functions, in response to detection of an abnormal state, which does not allow the secondary battery to be charged via the inverter. The power generation utilizing the counter electromotive force has stricter restrictions, for example, on the maximum power generation, compared with the power generation utilizing the inverter. The power generation utilizing the counter electromotive force is accordingly carried out in the state that does not allow the secondary battery to be charged via the inverter.
In the hybrid vehicle of the above application, when an observed voltage level of the secondary battery is higher than the counter electromotive force utilized for the power generation via the power generation control unit, one preferable arrangement prohibits the power generation utilizing the counter electromotive force via the power generation control unit but drives the motor with electric power accumulated in the secondary battery. In the case where the secondary battery has a sufficiently high voltage level as its state of charge, the motor may be driven with the electric power taken out of the secondary battery. During a drive of the hybrid vehicle, the secondary battery may be charged with the regenerative electric power. In such cases, the hybrid vehicle advantageously uses engine brake.
In the first hybrid vehicle of the present invention, the target revolving speed of the engine may be specified, based on behavior of an accelerator pedal. The behavior of the accelerator pedal is highly correlated to the power requirement of the vehicle expected in the near future. For example, depression of the accelerator pedal leads to an increase in required power to be output to the drive shaft. The arrangement of specifying the target revolving speed of the engine by taking into account such correlation enables the upper limit of energy output from the engine to be adjusted at an earlier timing. One preferable procedure increases the rotational speed of the generator with an increase in amount of depression of the accelerator pedal. The quick response to the increase in amount of depression of the accelerator pedal significantly improves the drivability.
In accordance with another preferable application of the present invention, the target revolving speed of the engine is lowered or raised in response to detection of an increasing tendency or a decreasing tendency of an actual revolving speed of the engine relative to the target revolving speed of the engine. The engine is under the feedback control to attain the target revolving speed. Controlling the driving state of the generator instantaneously increases or decreases the actual revolving speed of the engine. The control procedure of this application lowers or increases the target revolving speed of the engine in response to a variation in actual revolving speed of the engine. This anticipates a variation in loading in the near future. Such control is especially effective when separate control units are in charge of control of the engine and control of the generator and the motor and there is some interference with transmission of the target revolving speed between the separate control units, for example, via communication. The control procedure of this application may, however, be adopted in other structures that do not require transmission of the target revolving speed in such manner.
In the hybrid vehicle of the above application, one preferable control procedure urges the power generation utilizing the counter electromotive force, when an external force makes the drive shaft inversely rotated and the motor fall into a state of power generation. When there is an insufficiency of torque output from the vehicle, for example, running on a steep ascent, the vehicle may go back. In such cases, the drive shaft is inversely rotated and the motor falls into the state of power generation. The above control procedure desirably prevents over-voltage in such cases.
In the first hybrid vehicle of the present invention, one preferable control procedure sets a maximum electric power generated by the generator with the power of the engine, specifies driving electric power consumed for driving the motor within the preset maximum electric power, based on the specified loading. The control procedure drives the generator to generate electric power that is equivalent to the driving electric power consumed by the motor, and regulates the electric current running through a multiphase coil of the motor with the generated electric power. The control procedure of this application sets the maximum electric power generated by the generator and ensures the balance of the generated electric power with the consumed electric power within the preset maximum electric power.
The present invention is also directed to a second hybrid vehicle with an engine, a generator, and a motor mounted thereon, wherein the engine outputs power through combustion of a fuel, the generator generates electric power with at least part of the power output from the engine, and the motor outputs power to a drive shaft of the hybrid vehicle. The second hybrid vehicle includes: an engine control unit that feedback controls a quantity of the fuel injected to the engine to attain a specified target revolving speed of the engine; a generative energy computation unit that computes an instantaneous magnitude of generative energy to be generated by the generator by taking into account an energy balance in a system including the engine, the generator, and the motor; a voltage measurement unit that measures a generative voltage of the generator; a control variable computation unit that computes a feedback control variable corresponding to a difference between the observed generative voltage and a target generative voltage of the generator; a generator control unit that feedback controls the generator with the calculated instantaneous magnitude of generative energy and the calculated feedback control variable; a requirement detection unit that detects a requirement on a drive of the vehicle; and a motor driving unit that calculates an output torque of the motor based on a direct torque output from the generator, which is under control of the generator control unit, and a required torque related to the detected requirement on the drive of the vehicle, and drives the motor to attain the calculated output torque.
There is also a method of controlling the hybrid vehicle, which corresponds to the arrangement of the second hybrid vehicle. The present invention is accordingly directed to a second method of controlling a hybrid vehicle, wherein an engine outputs power through combustion of a fuel, a generator provided with permanent magnets generate electric power with at least part of the power output from the engine, and a motor is driven with at least part of the electric power generated by the generator, so as to output power to a drive shaft of the vehicle. The second method includes the steps of: feedback controlling a quantity of the fuel injected to the engine to attain a specified target revolving speed of the engine; computing an instantaneous magnitude of generative energy to be generated by the generator by taking into account an energy balance in a system including the engine, the generator, and the motor; measuring a generative voltage of the generator; computing a feedback control variable corresponding to a difference between the observed generative voltage and a target generative voltage of the generator; feedback controlling the generator with the calculated instantaneous magnitude of generative energy and the calculated feedback control variable; detecting a requirement on a drive of the vehicle; and calculating an output torque of the motor based on a direct torque output from the generator, which is under control of the generator control unit, and a required torque related to the detected requirement on the drive of the vehicle, and driving the motor to attain the calculated output torque.
The second hybrid vehicle of the present invention or the corresponding second method of controlling the hybrid vehicle carries out the control according to the calculated instantaneous magnitude of generative energy to be generated by the generator as well as according to the calculated feedback control variable. The instantaneous magnitude of generative energy is calculated by taking into account the energy balance in the system including the engine, the generator, and the motor. The feedback control variable is calculated corresponds to the difference between the observed generative voltage of the generator and a target generative voltage. Even when the generative voltage of the generator varies with a variation in loading, this arrangement ensures the quick response to such a variation and makes the quantity of energy generation balance with the quantity of energy consumption. This enables the hybrid vehicle to be driven without charging or discharging the secondary battery.
In accordance with one preferable application of the present invention, the generator uses permanent magnets to form a magnetic field, and the hybrid vehicle further includes: an inverter that switches electric current running through a multiphase coil of the generator; a secondary battery that is charged with the direct current converted by the switching operation of the inverter. The control procedure stops the switching operation of the inverter and causes the generator to carry out power generation utilizing a counter electromotive force, in response to detection of a state of failure in feedback control of the generator using the feedback control variable. In the case where the feedback control of the generator falls into the state of failure, this arrangement quickly stops this feedback control and causes the generator to carry out power generation utilizing the counter electromotive force. This arrangement effectively prevents the failure of the whole control. Although there is the upper limit, the power generation utilizing the counter electromotive force enables the power generation according to the quantity of power consumption and thereby makes the quantity of energy generation balance with the quantity of energy consumption. In the case where the feedback control of the generator through the switching operation of the inverter falls into the state of failure due to some disturbance, the temporary shift to the power generation utilizing the counter electromotive force effectively recovers the total state of control.
In the second hybrid vehicle of the present invention, in a specific driving state where the motor generates electric power, for example, in the course of braking, one preferable control procedure stops the fuel injection to the engine and causes the generator to motor the engine and thereby consume the electric power generated by the motor. This arrangement enables the hybrid vehicle to use engine brake.
The present invention is also directed to a third hybrid vehicle with an engine, a generator, and a motor mounted thereon, wherein the engine outputs power through combustion of a fuel, the generator generates electric power with at least part of the power output from the engine, and the motor outputs power to a drive shaft of the hybrid vehicle. The third hybrid vehicle includes: an engine control unit that feedback controls a quantity of the fuel injected to the engine to attain a specified target revolving speed of the engine; a secondary battery that is connectable with both positive and negative power lines of a direct voltage source, which link the generator with the motor; a first contact that switches on and off connection of the secondary battery with one of the two power lines and links the secondary battery with the power line via a restriction resistor, which restricts electric current flowing out of the secondary battery; a second contact that is connected to the first contact in parallel and directly links the secondary battery with the power line; a third contact that switches on and off connection of the secondary battery with the other of the two power lines; a weld detection unit that detects a weld of the third contact; and a welding-state driving unit that opens both the first contact and the second contact after activation of the engine in response to detection of the weld of the third contact, and drives the motor with the electric power generated by the generator.
There is also a method of controlling the hybrid vehicle, which corresponds to the arrangement of the third hybrid vehicle. The present invention is accordingly directed to a third method of controlling a hybrid vehicle, wherein an engine outputs power through combustion of a fuel, a generator provided with permanent magnets generate electric power with at least part of the power output from the engine, and a motor is driven with at least part of the electric power generated by the generator, so as to output power to a drive shaft of the vehicle. The third method includes the steps of: connecting a secondary battery with both positive and negative power lines of a direct voltage source, which link the generator with the motor; interposing a first contact between the secondary battery and one of the two power lines via a restriction resistor, which restricts electric current flowing out of the secondary battery; connecting a second contact to the first contact in parallel, the second contact directly linking the secondary battery with the power line: interposing a third contact between the secondary battery and the other of the two power lines; feedback controlling a quantity of the fuel injected to the engine to attain a specified target revolving speed of the engine; detecting a weld of the third contact; and opening both the first contact and the second contact after activation of the engine in response to detection of the weld of the third contact, and driving the motor with the electric power generated by the generator.
In the third hybrid vehicle of the present invention or the corresponding third method of controlling the hybrid vehicle, even when the third contact welds, once the engine is activated, the control procedure opens the first contact and the second contact and drives the motor with the electric power generated by the generator. This arrangement cuts off the connection of the power line with the secondary battery and thus protects the first contact and the second contact from welding during a drive of the vehicle. There is no necessity that the drive of the vehicle is prohibited, because of possible welding of the first contact and the second contact. This arrangement accordingly enhances the convenience of the user while maintaining the sufficient safety. The weld of the third contact is readily detected by setting a predetermined sequence to the on-off timings of the respective contacts and monitoring an inter-terminal voltage between terminals of the secondary battery and an inter-power line voltage between the positive and negative power lines of the direct voltage source.
In the third hybrid vehicle of the present invention, one preferable control procedure measures both then inter-terminal voltage between the terminals of the secondary battery and the inter-power line voltage between the two power lines and stops a drive of the vehicle when it is determined that the observed inter-terminal voltage is equal to the observed inter-power line voltage. This state suggests welding of the first contact or the second contact.
A diversity of structures are applicable to any of the first through the third hybrid vehicles of the present invention and the hybrid vehicles in the corresponding first through the third methods discussed above. Typical structures are a series hybrid vehicle and a parallel hybrid vehicle. In one preferable example, the generator has a pair-rotor structure including a pair of rotors rotatable relative to each other and carries out power generation to attain a voltage and electric power corresponding to a sliding rotational speed of the two rotors. This structure corresponds to an electrical distribution type parallel hybrid vehicle. There is also a mechanical distribution type parallel hybrid vehicle. In this structure, the generator is linked with one shaft of a three-shaft power distributor, in which power input to and output from one shaft is automatically determined when powers input to and output from residual two shafts are specified. One example of the three-shaft power distributor is a planetary gear mechanism. Another shaft of the three-shaft power distributor is linked with an output shaft of the engine and still another shaft of the three-shaft power distributor is linked with the drive shaft of the vehicle. The parallel hybrid vehicle uses part of the power output from the engine as the driving force of the drive shaft. This desirably reduces the size of the motor in the parallel hybrid vehicle.
In one applicable structure for any of the first through the third hybrid vehicles and the corresponding first through third methods, the generator is connected to a first electric power driving circuit that causes the generator to carry out either one of a generative operation and a power operation, based on an on-off state of switching elements included in the first electric power driving circuit, and the motor is connected to a second electric power driving circuit that causes the motor to carry out either one of a power operation and a generative operation, based on an on-off state of switching elements included in the second electric power driving circuit. This corresponds to the structure of a semiconductor inverter and ensures accurate control through regulation of the switching elements. Connection of the first electric power driving circuit with the second electric power driving circuit in this structure enables the hybrid vehicle to be driven in a battery-less drive mode that is free from the connection of the battery. It is, however, also practical to have a battery drive mode that is under the connection of the battery. In the latter case, a secondary battery or a high-capacity capacitor is connected to at least the first electric power driving circuit. Such connection enables the electric power generated by the generator to be accumulated in the secondary battery or the high-capacity capacitor.
In the structure that allows the hybrid vehicle to be driven in the battery-less drive mode, one preferable embodiment provides a cutoff unit that cuts off connection between the secondary battery and the first electric power driving circuit. At least when a generative voltage by the generator is higher than an inter-terminal voltage between terminals of the secondary battery, the cutoff unit is actuated to cut off the connection between the secondary battery and the first electric power driving circuit. In the battery-less drive mode, when the secondary battery has a low voltage level, part of the generated electric power may be used to charge the secondary battery. This reduces the amount of electric power used for driving. The arrangement of cutting off the connection between the secondary battery and the first electric power driving circuit by means of the cutoff unit enables all the generated electric power to be used for driving the motor.
In the hybrid vehicle of the above structure, in response to detection of a specific state that does not allow the secondary battery to be charged via the first electric power driving circuit, one preferable procedure drives the motor with electric current that is induced by a counter electromotive force generated between terminals of the multiphase coil of the generator through the operation of the engine and runs via a rectifier arranged in combination with each switching element in the first electric power driving circuit. Even in the case of malfunction of the switching element in the first electric power driving circuit, this arrangement assures power generation by the generator. In this structure, the generated electric power is autonomously determined according to the loading. This significantly facilitates the drive of the hybrid vehicle in the battery-less drive mode.